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All Forums >> Radios, Batteries, Clubhouse and more >> RC Radios, Transmitters, Receivers, Servos, gyros >> Radio Manufacturer Direct Support >> Polks Hobby >> Scanner sensitivity
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Scanner sensitivity - 3/30/2004 10:32:39 PM   
thojo


 

Posts: 216
Joined: 9/17/2002
From: Houston, TX,
Status: offline 		when flying RC combat, its not uncommon for between 4 to 6 to 12 radios to be on in close proximity on the flight line. I have found that in order to get my channel to come up. I have to turn the radio on with the antennia down.. What this effectively does is make the scanner a liability and not an asset.

Is there anyway to adjust the sensitivity of the scanner?
       Post #: 1

RE: Scanner sensitivity - 3/31/2004 7:48:44 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		thojo,
Oh, man, do I have this problem too. Paris was a nightmare, I was grounding my antenna every heat.

I've found that the best plan is to get your TX on early. I frequently ask the line marshall when we might fly, so I can get my TX on before everyone else. If you wait for the 90 seconds to be called, you'll never get your TX turned on in time. Between the long start up time, and all the radio noise in a big heat, the scanner goes nuts.

I also retract my antenna after landing each heat. This also helps keep me from breaking it in the close-packed pits (as I've seen happen to a few guys at times). And, as I said, when I turn on, I keep the antenna retracted. I also get it close to the grass, and point it downwards, or even touch it to the grass.

In a perfect world, I'd like to just disable the scanner when I'm at a contest. Contests have such tight frequency control anyway, it's not a threat.

It was cool seeing a fair handful of Polks at Paris though, I'd say about 10% of the pilots were flying one, and they still get a lot of interest in the combat community.


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to thojo)
       Post #: 2

RE: Scanner sensitivity - 4/2/2004 2:19:38 PM   
Cajun


 

Posts: 305
Joined: 4/21/2002
From: Nacogdoches, Tx
Status: offline 		I've had the same problem at three contests. It appears to be third order mod. We checked it out at Sulphur with a spectrum analyzer and the offending signal was real but no other radio was on that freq. The same thing was happening at Paris.

However at Paris there were two of us on 43 and I didn't bother getting the channel pin as I trusted the scanner to tell me if the other radio was on. It worked as designed. But I think the sensitivity could be reduced a little.

Cajun

(in reply to Montague)
       Post #: 3

RE: Scanner sensitivity - 4/2/2004 3:58:27 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Yeah, I'd love to see a graphic output from a spectrum analyzer during a combat contest. There must be spikes all over the place.

At Paris, I was on the same channel as 2 other guys, but I still just ignored the scanner and trusted the frequency control and impound.


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to Cajun)
       Post #: 4

RE: Scanner sensitivity - 4/2/2004 7:09:44 PM   
Cajun


 

Posts: 305
Joined: 4/21/2002
From: Nacogdoches, Tx
Status: offline 		In Paris, if I was up on the flite line with other radios operating close I would get the false signal from the scanner. If I was back in the rear of the pit area, all of the signals would be true.

Either our radios are generating some 3rd IM when operated that close together, or we have some radios being used that have drifted off freq.

It would probably be a good idea to borrow a spectrum analyzer from AMA for the large meets. These will not only tell you if a radio is on without the pin, but will also analyze the signal from all transmitters and point out the ones that are off frequency.

We had way too much unexplained radio problems in Paris.

Cajun

(in reply to Montague)
       Post #: 5

RE: Scanner sensitivity - 4/2/2004 7:27:24 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		That's odd, I didn't notice any radio problems in Paris. I didn't see anyone else having them either, but obviously I missed it if you had problems.

3IM and that sort of thing do get worse as the TXs get closer together. That's why the AMA has recommended min spaceing between transmitters. (which we routinely ignore).

FWIW, combat has one of the worst (if not the absolute worst) radio envrionments as far as intermodulation and such is concerned. We have so many radios going so close together. Sometimes I'm amazed that the gear works as well as it does.

As for the scanner. I only got false positives when I turned on the TX with the antenna up, and when I did that, I could pretty much always get a "hit" on my channel when people were flying. (I don't recall turning on back towards the tents though, only up forward.)

Signals strength does drop off as (if i recall?) the cube of the distance from the source, and 3IM signals are pretty weak to begin with, so I could easily believe that the scanner would notice it more on the flight line, right behind the transmitters, as opposed to farther away. (I forget, but I thought you were pitted towards the end as well, making your pit area that much farther from the operating transmitters? I was closer to the middle this time around)

Just keep that antenna down and pointed at the ground, and it's fine

I also would love to see the output from an alayser at a big contest. Not just a scanner that checks each channel, I want to see the whole 72Mhz spectrum, plus a bit on both sides. I bet the whole thing lights up like crazy, with lots of spikes in between channels and all kinds of stuff when we get a big heat going on. It would be even cooler if we could locate the antenna of the analyser out near the CEL, mid way down the flightline for a few heats, and then along the pilot line in a few places, as well as back in the pits. My guess here is that the IM effects are worst right at the flight line, while out past the CEL they'd drop off. That makes a late launch the worst case senerio from an RF perspective, I think.


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to Cajun)
       Post #: 6

RE: Scanner sensitivity - 4/3/2004 4:12:59 AM   
Cajun


 

Posts: 305
Joined: 4/21/2002
From: Nacogdoches, Tx
Status: offline 		We wern't having any serious radio problems on the S. end of the line, but the La. guys on the North end had some serious problems. It could well have been just a couple of bad radios, but I don't think they ever got a handle on it.

Lots of guys were complaining of interference Saturday, and since I was not flying B I turned my radio on scan and sat back in the pits and just monitored the freqs. Several guys were getting hit with interferience but when they came back to where I was the interference stopped and my scanner had not picked it up. I did not here of many complaints Sunday even though we were flying larger heats. Perhaps most of the guys had learned what was causing the problems.

I think your right in that we're just flying too close together.

Cajun

(in reply to Montague)
       Post #: 7

RE: Scanner sensitivity - 4/5/2004 5:54:26 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Yeah, if they are getting "hits" while everyone is close together, but nothing farther away, that sounds a lot like intermodulation or just swamping the RX/Scanner (pump out a powerful enough signal close enough to any RX, and you'll mess with it. I've accidentally confused my Supernova fast charger by leaning a powered-up TX with the antenna extended right next to it, for example).

They were packed awfully close on Saturday on the far end, it looks like they were pitted 3 deep in places.

Btw, what kind of radio problems were they having? Just problems with the Tracker picking up stuff? Or were the RX's actually going nuts?


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to Cajun)
       Post #: 8

RE: Scanner sensitivity - 4/5/2004 7:13:45 PM   
thojo


 

Posts: 216
Joined: 9/17/2002
From: Houston, TX,
Status: offline 		one thing I can say is last year at Paris, I got some nasty hits flying in some heats using my Hitec TX and this year on the Polk, I didn't have any problems whatsoever....

(in reply to Montague)
       Post #: 9

RE: Scanner sensitivity - 4/5/2004 7:21:54 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Were you using the same RX?

I've never had a "hit" during a combat match that I didn't later trace back to either a faulty RX, loose crystal, or bad battery. That's using both a Polk and my old JR TX.

I'm under the impression that most of our TX's have about the same output power, so it's mostly a matter of the RX sorting though all the noise and just looking at the correct signal. (I'm using a mix of Hitech 555, and FMA Extreme RX's. I'm hoping the new Polk mini RX will work in this role, but I suspect it will be a bit pricy for combat use)


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to thojo)
       Post #: 10

RE: Scanner sensitivity - 4/11/2004 5:44:33 PM   
Lewis Polk


 

Posts: 42
Joined: 9/18/2002
From: Irvington, NJ, USA
Status: offline 		Dear All,

Not to worry! Extend the antenna fully when setting the rx as at that point there is no transmission anyway. In track 1 the Tracker is working as a receiver only and there can be no transmission to bother anyone at all. I realize this is a tough concept to comprehend as no other radio does this, but in fact it's the key feature of the Polk Tracker. This is engineered to make it impossible to affect any other radio during set up and to protect all at the field as well as not letting you turn on when the frequency is in use.

Did I interpret your questions correctly?

All the best,
Lewis Polk

(in reply to Montague)
       Post #: 11

RE: Scanner sensitivity - 4/12/2004 12:34:02 AM   
causeitflies



Posts: 367
Joined: 1/1/2003
From: Steubenville, OH, USA
Status: online 		Lewis,
The scanner is so sensitive that when ever more than a few guys are flying (depending on the channels used) it is difficult to turn on the Tracker without getting the busy signal, even though no one is on that channel. Because of 3IM we sometimes have to take steps to bypass the scanner. It is picking up real interferance on that channel, but not enough to be a problem for the RX.

_____________________________

Mark P
An Expert has made every mistake - A Master has made every mistake twice

(in reply to Lewis Polk)
       Post #: 12

RE: Scanner sensitivity - 4/12/2004 4:03:46 PM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Lewis,
No, no one is worried about the Tracker shooting someone down or causing interference. It's not a "Track 1" issue at all.

The problem is as causeitflies mentioned, that the scanner picks up a lot of false-positives. Espeically when there are a number of other TX's on at once. For most guys, I suspect they never deal with more than 3-4 other TXs on at once, so they don't get much intermodulation interference.

However, some of us fly with quite a number of transmitters on at once. I've flown contests where there have been 12 other transmitters operating in fairly close proximity. And in those cases, the Tracker's scanner shows a lot of false positives.

It would be nice to be able to turn off the scanner, or override it, or at least turn down it's sensitivity in those cases.


_____________________________

Kirk Montague Adams
RCCA 560

(in reply to causeitflies)
       Post #: 13

RE: Scanner sensitivity - 4/23/2004 12:40:26 AM